Telephone system



w. WHITNEY 1,950,129

TELEPHONE SYSTEM Filed March 18, 1932 3 Sheets-Sheet l March 6, 1934.

March 6, 1934. w. WHITNEY 1,950,129

TELEPHONE SYSTEM Filed March 18, 1932 3 Sheets-Sheet 2 2/3 MAM/NAL 2Auna/NAL EL lg g /A/l/EA/TOR W. WH/ TNE y By A T TOR/VE V Filed March18, 1932 3 Sheets-Sheet 5 /Nl/ENTOR W W//T/VEy By A TTORNEV vun PatentedMar. 6, 1934 UNITED STATES PATET CFFCE TELEPHONE SYSTEM ApplicationMarch 18, 1932, Serial No. 599,656

l Claims.

This invention relates to a telephone system and more particularly to asystem in which an operator is enabled to intercept calls which havebeen extended to blank terminals of selector switches in theestablishment of either local or toll connections and to complete callsoutside the oiice in which the calls originated. The object of theinvention is to improve the apparatus of an intercepting operatorsposition in a system of this character whereby proper supervision may bepassed back from the selector switches which are employed to extend anintercepted call when the called subscriber answers to the switchesemployed by the calling subscriber in extending the connection to theoperato1"s position.

In the installation of telephone exchanges in which mechanical switchingmechanism is employed for extending connections between sub-- scriberslines, it is the usual practice to divide the exchange area into aplurality or" offices and to make provision in each oilice forultimately giving service to l0,000 subscribers lines. The number ofoiiices in the exchange is so selected that at the outset no cice isrequired to function t its ultimate capacity and therefore there may beswitching units which are not employed to their fullest extent. This isespecially true of incoming selector switches which have access to smallgroups or divisions of trunk lines and to iinal selectors which haveaccess to individual subscribers lines. Thus there will be a number ofterminal sets in the banks of incoming selectors Ywhich are blank or notconnected to Working trunk lines extended to final selectors andterminal sets in the banks of final selectors which are blank or notconnected to subscribers lines.

If an incoming selector switch in response to dialing is positioned toextend a connection into a division of an oice which has not yet beeninstalled, or a nal selector is positioned upon a blank terminal towhich no subscribers line has been connected, or upon the terminal of aline from which former service has been discontinued, or transferred toanother oce, the attempted connection is routed to `a trunk terminatingat an operators position on the A switchboard.

rIhe operator upon answering such a call with a cord circuit at herposition ascertains from the subscriber the number which he has calledand if he has dialed for a connection vto a particular subscribers linewhich has been given a new number terminating in another oflice of theexchange, she will proceed to extend the attempted connection throughher cord circuit over an outgoing trunk and selector switches to thedesired subscribers line in such other ofce.

When the connection has been thus established,

a talking circuit between the calling and called lines will exist overthe district, oice, incoming G0 and nal selectors in the originatingofice, the operators cord circuit and selectors in the terminatingoiice. For supervisory purposes, for example call charging, it isnecessary to pass a supervisory signal back to the district selector inthe originating cnice when the called subscriber answers. inasmuch asthe operators cord circuit is divided for transmission and supervisorypurposes by a repeating coil, it thus becomes necessary or desirable topass this answering supervisory signal around the repeating coil in thecord circuit.

In accordance with the present invention the cord circuit is providedwith a group of relays for thus passing back an answering supervisorysig- 'I6 nal which functions when reverse battery is connected to thecalling end of the cord circuit from the incoming selector in theterminating oce following the response of the called subscriber. Should,however, the called line be busy and a busy-back iash be transmittedfrom the terminating cnice, the group of relays is arranged not to passa supervisory signal back to the orignating cnice.

This group of relays comprises arst relaywhich operates when thepolarized supervisory relay of the cord circuit operates on reversebattery and prepares the circuit of a pick-up relay which operates overthe back contacts of an interruptor when the interruptor reaches aposition in which such contacts are closed. The pick-up relay whenoperated, locks and prepares a circuit for a third relay which in turnoperates over the front contacts of the interruptor as soon as theinterrupter has advanced to close its front contacts. When the thirdrelay operates, it closes a low resistance bridge across the answeringend of the cord circuit for establishing a supervisory loop back to thedistrict selector in the originating otlice. This supervisory loopaccomplishes the same function as though the iinal selector in theoriginating oiiice had succeeded in terminating the connection on theterminals of the desired line and the subscriber whose line wasconnected thereto had responded in the usual manner.

The manner in which the invention functions will be more evident fromthe following detailed description taken in connection with theaccompanying drawings in which:

Fig. 1 shows schematically a calling subscribers 110 line, line iinder,district, incoming and final selector switches, a sender in which thecalling subscriber may cause the registrations of line designations andwhich in accordance with such registrations causes the setting of theselector switches, and an intercepting trunk circuit accessible from theiinal selecto-1' switch and terminating at the operators position ofFig. 2;

Fig. 2 shows one lcord circuit of an operators position by means ofwhich the operator may render assistance and intercepting service tocalling subscribers;

Fig. 3 shows the telephone and keyset circuits of the operatorsposition;

Fig. 4 shows schematically a trunk ycircuit terminating in an ofceselector, incoming and final selector switches, a called subscribersline and a sender under the control of the operators keyset forcontrolling the selector switches for enabling the operator to completeconnections; and

Fig. 5 is a diagram showing the manner in which the remaining iiguresshould be arranged to show the complete circuits of the invention.

The cord circuit of Fig. 2 located at the A operators position hasaccess over the answering plug 201 to jacks of incoming trunks whichmay, for example, be intercepting trunks from final selector multiplesas disclosed in Fig. 1, or from incoming selector multiples, or trunksincoming from district or oflice selector multiples over which callingsubscribers have made calls for assistance in establishing connectionsor tie line trunks from. other operators positions or manual subscriberslines. Over the calling plug 221 of the Y' cord circuit the operator mayhave access to different groups of trunk circuits for completingconnections. These groups of outgoing trunk circuits may be of the typedisclosed in the application of W. B. Strickler, Serial No. 599,684,filed concurrently herewith, now Patent No. 1,897,083, granted Feb. 14,1933. For the purposes of this description it will be assumed that thetrunk circuit employed and disclosed schematically in Fig. 4 is of thetype terminating in an oflice selector switch. The keyset and operatorsposition equipment shown in Fig. 3 is common to all of the cord circuitssuch as the cord circuit of Fig. 2 of the operators position. The senderschematically shown by the rectangle in Fig. 4 is of the type disclosedin the aforementioned application of W. B. Strickler and is controlledfrom `the operators keyset in the manner fully described there- It willbe assumed that the calling subscriber 100 initiates a call for aconnection to a subscribers line, the number of which is listed in thetelephone directory, but which line has been given a new number assignedto another office of the exchange area. In response to the removal ofthe subscribers receiver from the switchhook, his line becomes connectedin the well-known manner by means of the line iinder 101 to a sender102- Upon receiving the usual dial tone from the sender the subscriberthen proceeds to dial the digits of the designation of the desired line.The sender 102 registers the dialed digits and proceeds to set theselector switches 103, 104 and 105 to extend a connection to theterminals of the desired line. Since, as has been assumed, the desiredline has been disconnected from the terminals upon which the finalselector switch 105 has been set, the final selector makes connectionwith the terminals of an intercepting trunk which has been connected inlieu of the subscribers line.

A circuit is therefore established from ground in the final selector,over the sleeve brush 106 thereof, sleeve terminal 107 of the trunk,lower back contact of relay 108 to battery through the winding of relay109. Relay 109 operates and locks directly to ground on sleeve terminal107 and closes a circuit for trunk lamp 235 extending from battery,upper front contact of relay 109, upper back contact of relay 108,conductor 110 to ground through lamp 235. The operator upon noting theillumination of lamp 235 inserts plug 201 into jack 200 therebyestablishing a circuit from ground through the lower winding of relay108, conductor 111, sleeves of jack 200 and plug 201 to battery throughthe winding of relay 202 and the winding of marginal relay 203 in seriesand to battery in parallel therewith through the non-inductive winding204 of relay 203. Relay 108 operates in this circuit locking over itsupper winding and upper front contact, the upper front contact of relay109 to battery opening at its upper back contact the vcircuit of lamp235 thereby extinguishing the lamp. At the cord circuit relay 202operates but due to the high resistance of the lower winding oi? relay108, marginal relay 203 does not operate. Relay 202 upc-n operatingcloses a circuit for the supervisory lamp 205 extending from battery,over the inner contact of relay 202, resistance 206, back contact ofrelay 207, back contact of relay 208 to ground through lamp 205 and inparallel therewith from battery over the inner contact of relay 202,resistance 206, back contact of relay 207, back contact of relay 208,inner lower back contact or relay 209, inner normal contacts and windingof relay 210 to ground at the lower right normal contact of key 211.Relay 2l0 locks in a circuit from battery at the inner contact of relay202, inner upper alternate contacts and winding of relay 210 to groundat key 211. The operator now throws her talking key 211 to the rightopening the circuit of relay 210 which releases, and closing an obviouscircuit for relay 217 which in turn establishes a circuit from battery,over the inner contact of relay 202, inner lower contact of relay 217,conductor 236 to ground through the winding of relay 339. Ringingcurrent applied from the incoming selector 104 now flows over the ringbrushes of incoming selector 104 and final selector 105, trunk conductor112, rings of jack 200 and plug 201, lower normal contact of key 214,lower left winding of repeating coil 213, inner lower back contact ofrelay 203, middle lower back contact or" relay 209, middle lower contactof relay 217, conductor 237, back contact of relay 340, resistance 341,winding of relay 342 to ground at the outer contact of relay 339. Relay342 responds to the ringing current closing a circuit from ground at itscontact, through the contacts of interrupter 343, back Contact of relay344 to battery through the winding of relay 345. Relay 345 operates andlocks through its winding, the winding of relay 344, the outer frontcontact of relay 345 to ground at the contact of relay 342, but relay344 being shunted does not operate until the interrupter 343 opens itscontacts. Relay 345 at its inner contact closes an obvious holdingcircuit for relay 342 and thereby increases the current iiowing o-verthe ringing circuit from the incoming selector to such an extent as tocause theV disconnection of the ringing current supply at the incomingselector and the cutting through of the talking circuit at the incomingselector.

VAs soon as the talking circuit is cut through Vat the incomingselector, a circuit is established from ground through the upper rightwinding of repeating coil 114, tip brushes of incoming selector 104 andfinal selector 105, trunk conductor 113, tips of jack 200 and plug 201,upper normal contact of key 214, upper left winding of repeating coil213, upper back contact of relay 203, lower low resistance winding ofrelay 208, lower back contact of relay 209, upper back contact of relay241 to battery through resistance 240 thus operating relay 208 which atits back contact extinguishes lamp 205. A circuit is also establishedfrom grounded battery through the lower right winding of repeating coil114, winding of supervisory relay 115, ring brushes of incoming selector104, and final selector 105, conm ductor 112, rings of jack 200 and plug201, lower normal contact of key 214, lower left winding of repeatingcoil 213, lower back contact of relay 203, intermediate lower backcontact of relay 209, resistance 242 to ground at the inner upper backcontact of relay 240. Resistance 242 is high and therefore supervisoryrelay 115 at the incoming selector does not operate in this circuit.

When relay 344 operates and the interruptor contacts again close, relay340 operates in a circuit extending from battery through its winding,the front contact of relay 344, contacts of interrupter 343 to ground atthe front contact of relay 342. Relay 340 upon operating locks to groundat the iront contact of relay 339, opens the initial operating circuitof relay 342 and. closes a circuit extending from ground at its leftcontact, through the upper winding of relay 300 to battery.

Relay 300 operates and a talking path is thereupon established from theupper right winding of repeating coil 213, inner upper right contact ofkey 211, conductor 219, upper contact of relay 300, right winding or"repeating coil 301, condenser 302, lower contact or" relay 300,conductor 220, inner lower right contact of key 211 to the lower rightwinding of coil 213. Assuming that the operators telephone set 303 isplugged up, the talking path just traced is inductively associatedtherewith through the left winding of repeating coil 301 and. theoperator is thereupon enabled to converse with the calling subscriber toascertain information concerning the connection which he has attemptedto coniplete.

It will be assumed that the line of the desired subscriber may bereached over the trunk circuit and selector switches disclosed in Fig. 4and that therefore the operator first tests the trunk circuit bytouching the tip of calling plug 221 to the sleeve of jack 400 of thetrunk circuit. If the trunk circuit is busy, there will be batterypotential on the sleeve thereof and this potential will be transmittedover the tip or" plug 221, the upper normal contacts of relay 222, theinner upper back contact of relay 223, the upper normal contact of key224, conductor 225, condenser 304 to ground through the right winding ofrepeating coil 305 which induces busy potential through the left windingof coil 305 and the back contacts of relay 348 into the cperatorstelephone set thus producing a click in her receiver. Assuming that shends the trunk circuit of Fig. 4 idle and receives no click, she insertsthe plug 221 into jack 400, thereby establishing a circuit eX- tendingfrom ground through the winding of sleeve relay 401 of the trunkcircuit, sleeves of jack 400 and plug 221, windings of relay 226 andmarginal relay 227 in series to battery and in parallel therewiththrough resistance 228 to battery. Due to the high resistance of sleeverelay 401, suiiicient current flows to operate relay 226, but marginalrelay 227 does not operate.

Relay 226 upon operating closes a circuit ex tending from battery overits lower Contact, the lower normal contact of key 224 to ground throughthe Winding of relay 223 which operates opening the busy test circuit atits upper back contact and at its inner upper' and inner lower frontcontacts connects the tip and ring contacts of plug 221 to the rightwindings of repeating coil 213. Relay 226 at its lower contact alsoestab'- lishes a circuit for lamp 229 extending over the upper backcontact of relay 230. Preparatory to keying the digits necessary tocomplete the connection, the operator now depresses the key 306 and withthe talking key 211 operated to the right, a circuit is established fromground at the lower back contact of relay 308, the right contact of key306, conductor 307, the lower and upper intermediate alternate contactsof key 211, the upper winding of relay 222 to battery at the lowercontact of relay 223. Relay 222 thereupon operates and locks in acircuit from battery over the lower contact of relay 223, lower windingand inner lower iront contact of relay 222, conductor 231, back contactof relay 309 and in parallel to ground through resistance 310 and thewinding of relay 308. Relay 308 operates in this circuit opening theinitial operating circuit of relay 222 and closing an obvious circuitfor relay 311 which operates. Relay 222 at its upper and lower alternatecontacts disconnects the tip and ring contacts of plug 221 from theright windings of repeating coil 213 and connects these contacts overconductors 232 and 233 with the operators keyset circuit.

Relay 311 upon operating closes an obvious circuit to light lamp 312,connects ground over conductor 313 for supplying operating ground to thekeys of the keyset 314 and establishes a circuit from ground at itsupper contact, through the winding and upper normal contacts of relay315, conductor 232, upper alternate contacts of relay 222, tips of plug221 and jack 400 to battery through the winding of the start relay, notshown, of the trunk circuit of Fig. 4. As described in the applicationor W. B. Strickler hereinbefore mentioned, the operation of the startrelay of the trunk circuit causes the association of the trunk circuitwith an idle sender such as that shown schematically at 402 in Fig. 4.As soon as the sender 402 has been attached to the trunk circuit, acircuit is established from ground at the sender over the ring conductor403 of the trunk circuit, ring contacts of jack 400 and plug 221, `loweralternate contacts of relay 222, conductor 233, upper normal contacts ofrelay 317, resistance 316 to battery. A relay in the sender operates inthis circuit and closes a circuit from battery at the sender over thetip trunk conductor 404, tips of jack 490 and plug 221, upper alternatecontacts of relay 222, conductor 232, upper normal contacts and windinfrof relay 315 to ground at the upper Contact of relay 311. Relay 315operates in this circuit locking over its upper alternate contactsthrough resistance 316 to battery and also closes a circuit from groundat the upper contact of relay 311, upper back contact oi relay 318 lowercontact of relay 315 to battery through the Winding of relay 317. Relay317 upon operating connects 48-volt battery through resistance 319 andthe lower iront contact of relay 317 to conductor 320 for supplyingbattery to key contacts of keyset 314 and connects the keyset over itsinner lower front and upper alternate contacts to conductors 232 and 233and thence to the sender. Relay 315 also closes a circuit extending fromground at the upper contact of relay 311, upper back contact of relay318, lower front contact of relay 315, lower back contact of relay 318to battery through lamp 321. Lamp 321 lights to indicate to the operatorthat the sender 402 is in condition to register the digits of thedesired line designation.

The operator now proceeds to set up on the keys of her keyset 314 thecnice code and numerical designations of the subscribers line 405 towhich connection is to be extended and then depresses the start key 332.Through the operation of the keys of the keyset and the operation of thestart key, registers of the sender 402 are set and a start combinationis registered for starting the sender to function to establish thedesired connection. Since the manner in which this is accomplished isnot pertinent to the present invention, reference may be had to theaforementioned application of W. B. Strickler for a detailed dcscriptionof the manner in which the sender functions in response to the keyset toregister the line designation and to set the oflice selector 406, theincoming selector 407 and the nal selector 408 to extend the desiredconnection to the subscribers line 405. Following the registration ofthe start combination in the sender in response to the operation ofstart key 332, the sender connects 24-volt battery to both the tipconductor 404 and the ring conductor 403 of the trunk circuit therebycausing the operation of the two polarized relays 333 and 334 of theoperators keyset circuit. With both of these relays operated an obviouscircuit is closed for relay 335 which locks to ground at the uppercontact of relay 311 and connects ground over its upper contact to thesender over the tip trunk conductor 404 which causes the operation of arelay in the sender to remove 24-volt battery from the operatingcircuits of relays 333 and 334. Relay 333 now releases, but relay 334 isheld operated by relay 335. Relay 333 upon releasing closes a circuitfrom ground at its back contact, lower front contact of relay 335,winding of relay 309 to battery. Relay 309 operates and f opens thecircuit of relay 308 which upon releasing in turn releases relay 311.Relay 311 upon releasing in turn releases relays 335, 334, 309, 315 and317 and extinguishes lamps 312 and 321. Relay 311 upon releasing alsoreleases relay 222 in the cord circuit. The operators keyset circuit visnow in normal condition.

If the operator disregards the pilot lamp 321 and starts keying adesignation before the sender is attached and relay 317 has beenoperated from the sender a circuit will be closed for relay 318 frombattery through its winding, inner lower back contact of relay 317,conductor 327 to ground on conductor 313 through contacts of any oper-Vated key of the keyset 314. Relay 318 upon operats ing locks over theleft contact of key 306, upper front contact oi relay 318 to ground atthe upper contact of relay 311 and at its lower iront contact connectslamp 321 in a flashing circuit through the contacts of interrupter 336.To prepare the keyset for use, the operator must depress key 306 torelease relay 318.

' Following the operation of the sender to set the selector switches ofFig. 4, the sender 402 is released and a talking circuit is establishedover Vtrunk conductors 403 and 404 and the brushes of oiiice selector406 to the incoming selector 407, this talking circuit extending fromthe tip trunk conductor 404 over the tips of jack 400 and plug 221,upper normal contacts of relay 222, which released when the operatorskeyset was released following completion of keying, inner upper frontcontact of relay 223, upper right winding of repeating coil 213, upperback contact of relay 227, upper front Contact of relay 223, winding ofpolarized supervisory relay 234, lower back contact of relay 227, lowerright winding of repeating coil 213, inner lower front Contact of relay223, lower normal contacts of relay 222, rings of plug 221 and jack 400to the ring trunk conductor 403.

When the called subscriber 405 answers current flowing over this talkingpath from the incoming selector is reversed in the well-known mannerthereby causing the operation of polarized relay 234. Relay 234 causesthe operation of relay 230 over an obvious circuit which in turn at itsupper back contact opens the circuit vof calling supervisory lamp 229.Relay 230 at its inner lower front contact establishes a circuit fromground as soon as interrupter 238 closes its left contact, through theupper normal contacts and winding of pick-up relay 239, lower backcontact of relay 203 to battery at the lower contact of relay 202. Relay239 operates and locks over its upper alternate contacts to ground atthe upper front contact of relay 230 and as soon as interrupter 238closes its right contact, establishes a circuit from ground at the rightcontact of interrupter 238, intermediate lower front Contact of relay230, lower front contact of relay 239, upper normal contacts and windingof relay 209, lower back contact of relay 203 to battery at the lowercontact of relay 202. Relay 209 operates and locks directly to groundover its upper alternate contacts independent of the contacts ofinterrupter 238, opens the circuit previously traced from batterythrough the lower winding of relay 208 to ground at the incomingselector 104 and the circuit previously traced from grounded batterythrough the winding of supervisory relay 115 at the incoming selectorand establishes a loop circuit extending from ground through the upperright winding of repeating coil 114, thence as traced through the lowerwinding of relay 208, lower front contact of relay 230, lower frontcontact of relay 209, thence as traced through the winding ofsupervisory relay 115 and the lower right winding of repeating coil 114to battery. The current flowing over this circuit is now sufficient tooperate relay 115 which then, in the well-known manner, controls theestablishment of a supervisory condition in the district selector 103indicating thereat that the called subscriber has answered the call. Theupper high resistance winding of relay 208 is at this time shunted overthe lower contact of relay 230.

1i when the connection is made to the terminals of the called line 405,such line is busy, then the final selector 408 would in the ,wellknownmanner place a busy tone current on the talking circuit thereat, whichtone current is transmitted through the windings of the repeating coil213 and thence to the calling subscribers line over the establishedconnection and the calling supervisory relay 234 is intermittentlyoperated to thereby intermittently operate relay 230 to flash thecalling supervisory lamp 229. Since in this case relay 230 does notremain operated steadily, pick-up relay 239 does not have time ing ofrelay 344.

to operate from the interrupter 238 and remain locked so that relay 209may be operated from the interrupter and locked and, consequently, thesupervisory circuit established through the operation of relay 209 aspreviously described, is not rendered effective. It is thus apparentthat the incoming selector 104 receives a supervisory signal upon theresponse of the called subscriber and not when the called line is foundto be busy and a busy signal is sent to the operators position.

Upon the termination of the conversation, the calling and calledsubscribers restore their receivers to the switchhooks. When the callingsubscriber hangs up the line nder 10i., district selector 103, incomingselector 184 and nnal selector 105 release in the well-known manner inturn releasing relay 109 and opening the locking circuit of relay 108.Until the operator withdraws plug 201 from jack 200, relay 108 remainsoperated and busy potential is maintained on the sleeve terminal 107 toprevent other final selectors from seizing the incoming trunk. rThisbusy potential is applied over a circuit traceable from the sleeveterminal 107, the lower front contact of relay 108, lower back contactof relay 109, resistance 116, inner lower front contact of relay 108 tobattery and from the lower back contact of relay 109 through resistance117 to ground at the inner upper back contact of relay 109. rlhe releaseof the incoming selector 104 and iinal selector 105 also opens thepreviously traced circuit through the lower winding or" relay 208whereupon relay 208 releases again closing the circuit of the answeringsupervisory lamp 205.

When the called subscriber hangs up, the polarized supervisory relay 234releases in turn releasing relay 230 which at its upper contact closesthe previously traced circuit for calling supervisory lamp 229 and atits inner upper front contact opens the locking circuit or relay 239which then releases. The operator upon noting the lighted lamps 205 and229 withdraws the plugs 201 and 221 from jacks 200 and 400 releasing alloperated relays of the cord circuit and releasing relay 108 of theincoming trunk circuit and relay 401 of the outgoing trunk circuit ofFig. 4. Relay 108 upon releasing removes the busy potential from thesleeve terminal 107 of the incoming trunk thereby rendering it againselectable. Relay 400 upon releasing restores the operated apparatus ofthe outgoing trunk and the selectors of Fig. 4 release in the well-knownA manner.

Should the operator desire to monitor on an established connection, shemay do so by throwing key 211 to the left thereby closing a circuit fromground, over the lower left contact of key 211, conductor 243 to batterythrough the wind- The tip and ring conductors or the cord circuit arenow connected over the upper and intermediate left contacts of key 211,conductors 244 and 245, through the right winding of repeating coil 345and thence inductively over the left winding of coil 345, inner upperand lower front contacts of relay 344 to the operators telephone set303.

If the desired subscribers line is one terminating in a manual oi'ice,then the operator connects the calling plug 221 to the jack of a trunkcircuit terminating in the manual oice. Such runk circuits are providedwith low resistance sleeve relays and consequently upon the insertion ofplug 221 in the jack of such a trunk circuit the current nowing throughthe windings of relays 226 and 227 is of sufficient strength to operateboth of these relays. In this case since it is not necessary to key thecalled line designation, the operator does not depress key 306 of herkeyset circuit and relay 222 is therefore not operated. Relay 226 uponoperating causes the operation or" relay 223 and the lighting of lamp aspreviously described. 1n case the operator desires to ring the calledsubscriber, she depresses the ringing key 224 thereby releasing relay223 and closing a ringing circuit from ringing generator 246, over theupper alternate contact of key 224, upper back contact of relay 223,upper normal contacts of relay 222, thence over the establishedconnection returning over the lower normal contacts of relay 222, lowerback contact of relay 223, lower alternate contacts or key 224 toground'. When the ringing key 224 is again restored and relay 223 againoperates, and with marginal relay 227 operated, a supervisory circuit isestablished upon the response of the called subscriber which may betraced in part from battery, right winding of retard coil 247, windingof supervisory relay 248, lower front contact of relay 227, lower rightwinding or repeating coil 213, inner lower front contact of relay 223,lower normal contacts of relay 222, thence over the establishedconnection and returning over the upper normal contacts of relay 222,inner upper front contact of relay 223, upper right winding of repeatingcoil 213, inner upper front contact or" relay 227 to ground through theleft winding-oct retard coil 247. Relay 248 operates in this circuitVclosing an obvious circuit for relay 230 which in turn opens the circuitof supervisory lamp 229. When the calling and called subscribers restoretheir receivers to the switchhooks upon the termination or" theconversation, the supervisory lamps 205 229 light in the mannerpreviously described and the operator noting the illumination of theselamps withdraws the plugs 201 and 221 from the trunk jacks and therestoration of all apparatus employed in the connection is eirected inthe manner previously described.

1f the call incoming to the operators position is one initiated over atie line from a manual operators position and the intercepted operatordesires to flash the manual operator she may do so'by depressing the key214 thereby opening the supervisory circuit extending over the answeringplug 201 and operating slow-to-release relay 250. When key 214 is againreleased and during the releasing time or relay 250 a resistance bridgeis closed from the tip contact of plug 201 through the upper leftwinding of repeating coil 213, upper back contact of relay 203, contactof relay 250, resistance 249, middle lower back contact of relay 209,inner lower back contact of relay 203, lower left winding of repeatingcoil 213 to the ring contact of plug 201. The connection ci this bridgeextinguishes the supervisory lamp at the manual operators cord circuit.The repeated operation and release of the flashing key -f'L- 214 causesthe manual operators supervisory lamp to be iiashed in unison with thekey.

Should the manual operator or a subscriber desire to rlash theintercepting operator to recall the operator after she has restored hertalking key 211, this may be done by momentarily opening the supervisorycircuit incoming over the answering plug 201 of the interceptingoperators cord circuit, thus opening momentarily the circuit of relay207 if relay 203 was operated in ist ist

answering the call, or opening the circuit of relay 208 ii" relay 203was not operated. With either of these relays released the previouslytraced circuit for relay 210 is closed and relay 210 locks to ground atthe right normal contact of key 211 and the circuit of lamp 205 isclosed from ground, inner lower back contact of relay 209, upper frontcontact of relay 210, resistance 206 to battery at the lower contact ofrelay 202. As soon as either relay 207 or relay 208 reoperates when theincoming supervisory circuit is again established, With relay 207operated, an intermittent shunt is established around lamp 205 extendingfrom ground through contacts of interrupter 216, lower contact of relay210, front contact of relay 208 to ground through lamp 205 or over thefront contact of relay 207, back contact of relay 208 to ground throughlamp 205 dependent upon whether relay 207 or relay 208 is at the timeoperated. Lamp 205 flashes as a recall signal. As soon as the operatornotes the finishing lamp she throws her key 211 for listening and relay210 releases opening the ashing circuit of lamp 205.

What is claimed is:

1. In a telephone exchange system, a calling line, a trunk circuitincoming to an operators position, selector switches for extending aconnection from said line to said trunk circuit, a cord circuit at saidposition for connection to said trunk circuit, a called line, anoutgoing trunk circuit accessible to said cord circuit and otherselector switches for extending a connection from said calling line oversaid iirst selector switches and said cord circuit to said called line,a supervisory relay in said cord circuit operable upon the response or"said called subscriber, and means controlled by said relay after apredetermined interval for transmitting a supervisory signal to one ofsaid rst selector switches.

2. In a telephone exchange system, a calling line, a trunk circuitincoming to an operators position, selector switches for extending aconnection from said line to said trunk circuit, a cord circuit at saidposition for connection to said trunk circuit, a called line, anoutgoing trunk circuit accessible to said cord circuit and otherselector switches for extending a connection from said calling line oversaid rst selector switches and said cord circuit to said called line, asupervisory relay in said cord circuit, and means including a group ofrelays and an interrupter conline, an outgoing trunk circuit accessibleto said cord circuit and other selector switches for extending aconnection from said calling line over said first selector switches andsaid cord circuit to said called line, a supervisory relay in thecalling end of said cord circuit operable upon the response of saidcalled subscriber, and means controlled by said relay after apredetermined interval for closing a supervisory circuit over theanswering end of said cord circuit to one of said first selectorswitches.

4. In a telephone exchange system, a calling line, a trunk circuitincoming to an operators position, selector switches for extending aconnection from said line to said trunk circuit, a cord circuit at saidposition having a repeating coil for connection to said trunk circuit, acalled line, an outgoing trunk circuit accessible to said cord circuitland other selector switches for extending a connection from said callingline over said iirst selector switches and said cord circuit to saidcalled line, a supervisory relay in the calling end of said cord circuitoperable upon the response of said called subscriber, an interrupter, apickup relay operable by said interrupter following the operation ofsaid supervisory relay, a third relay operable by said interrupterfollowing the operation of said pick-up relay, and a supervisory circuitextending over the answering end of said cord circuit to one of said rstselector switches controlled by said third relay.

WILEY WHITNEY.

